Diesel engines have different operating conditions than spark-ignition engines. They rely on different thermodynamic principles and different fuel cycles. Power is mostly controlled by a regulation of the fuel supply directly, not by the control of the air supply. When diesel engines run at low power, the mixture and combustion is not deprived of oxygen and few by products are created, but when load or effort (W) is added to these engines, a greater amount of carbon monoxides and impurities are produced.
In these systems, the fuel mixture is starved for oxygen to levels as low as 5% of the needed stoichiometric mixture or having a equivalence ratio of 20 to 1. The equivalence ratio (Φ) being defined as Φ=1/(oxygen levels/stoichiometric mixture oxygen levels) and where Φ=20 for a fuel starved at 5% of needed oxygen. The term stoichiometry is a calculation of a quantitative relationship of the reactants and the products in a balanced chemical reaction. If the oxygen level is at a stoichiometric mixture level, or a mixture where the equivalence ratio is 1, all of the given products and reactants are used by the chemical reaction. What is desired is a equivalence ratio as close to 1 as possible. Air fuel ratios of common fuels, include 14.7:1 for gasoline, 17.2:1 for natural gas, and 14.6:1 for diesel fuel. In mass these ratios correspond to 6.8%, 7.9%, and 6.8% respectively.
While oil refineries may help with removing sulfur and lead from the fuel and ultimately reduce associated emissions, systems forced to operate at fuel staved regimes must develop other processes to reduce soot emissions, fine particles, and nanoparticles found in the exhaust gasses of these engines while increasing their overall thermal efficiency of the engine. For example ceramic soot filters or other after burning system can be used in an effort to decrease unwanted emissions. What is needed is a system that may be inserted within the existing system and not external to the system to reduce soot emissions, and increase thermal efficiency of the engine.
While this invention is directed to any thermodynamic combustion cycle and related combustion device, and any device or engine, this disclosure describes mainly a current best mode directed at the diesel cycle for diesel combustion engines as invented by Rudolph Diesel in 1897. The concepts described here, when applicable are also used in other combustion cycles and other thermodynamic based devices.
The ideal diesel cycle is a four phase loop generally illustrated by a Pressure (P) v. Specific volume (V) diagram. In a first phase of the process, a compression is made at an isentropic regime, consequently the specific volume is decreased from V1 to V2 as the pressure is increased from P1 to P2. (Where the subscript is the number of the position of on the four step cycle). Work is done Win in this phase for example by a piston compressing a working fluid such as air. In the second phase of reversible constant pressure heating, heat Qin is added via the combustion of the fuel at constant pressure P2. The specific volume V increases a small fraction from V2 to V3 during this second phase. In a third phase of the process known as the isentropic expansion phase, work is released Wout by the working fluid expanding on the piston creating a torque at a cam. During this phase, the pressure drops from P2 to P4 and the specific volume is increased to its maximum from V3 back to V1. Finally, in the fourth and last phase, the system is returned to the starting point in a reversible constant volume cooling by taking out heat Qout by venting the air out of the piston from a pressure P4 to the initial pressure P1, thus returning the system to the P1, V1 configuration.
Thermal efficiency (ηth) of the diesel fuel cycle is dependant upon several parameters including a compression ratio (r) and a cut-off ratio (α). The cut-off ratio (α) is defined as a ratio between the end and start volumes of the combustion phase α=V3/V2, and the compression ratio (r) is defined as r=V1/V2. Finally, a ratio of specific heats (γ) is used as part of the thermal efficiency calculation and is defined as γ=CP/CV. The ideal thermal efficiency for a diesel cycle is given as:
      η    TH    =      1    -                  1                  r                      γ            -            1                              ⁢              (                                            α              γ                        -            1                                γ            ⁡                          (                              α                -                1                            )                                      )            
Thermal efficiency can also be calculated using temperatures instead of volumes since V3/V2=T3/T2 where T3 is the temperature of the fluid at the end of the third phase of the cycle and T2 is the temperature of the fluid at the end of the second phase of the cycle. What is desired is an effective cycle operating as close to thermal efficiency of 1 as possible (i.e. where the factor in the equation drops to 0).
Further, since hydrocarbons (HC) are released as part of the exhaust gasses, the thermal efficiency is lowered by this unburnt fuel released to the atmosphere in the overall cycle since a portion of the fuel is not used. Further, exhaust gas is emitted as a result of the combustion of fuels such as natural gas, gasoline, petrol, diesel, fuel oil, coal, etc. A large proportion of exhaust gas is discharged into the atmosphere through exhaust pipes, gas stacks, or propelling nozzles. Exhaust gasses are made mostly of harmless nitrogen (N2), water vapor (H2O), and carbon dioxide (CO2), along with a small part of undesirable noxious or toxic substances, such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), other partly unburnt fuel, and particulate matter (soot). Exhaust gasses of diesel engines may also contain a complex and harmful cocktail of impurities. For example, these gasses also include lead (Pb), or even sulfuric dioxides (SOj).
Exhaust fumes are used and recycled in an effort to limit knocking or lowering of the combustion point temperature in the cylinder. Further, exhaust gas reintroduced as fuel recycle unburnt HC particles and reduces the overall emission of unburnt particles associated with a oxygen deprived starvation combustion process. What is needed is a way system of introduction of oxygen into a oxygen deprived, rich mixture fuel cycle engine that improves thermal efficiency, lowers unwanted emissions, and soot particles without adversely affecting the engine performances.